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  • PANGAEA  (101)
  • Macmillian Magazines Ltd.  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 779-782 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The surface waters of the modern subarctic Pacific Ocean are isolated from the nutrient-rich waters below by a steep vertical gradient in salinity (halocline), a feature which is a dominant control on upper-ocean stratification in polar environments. The physical processes which maintain the ...
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] To explain the lower atmospheric CO2 concentrations during glacial periods, it has been suggested that the productivity of marine phytoplankton was stimulated by an increased flux of iron-bearing dust to the oceans. One component of this theory is that iron—an essential ...
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  • 3
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    PANGAEA
    In:  Supplement to: Pichevin, Laetitia; Ganeshram, Raja S; Francavilla, Stephen; Arellano-Torres, Elsa; Pedersen, Thomas F; Beaufort, Luc (2010): Interhemispheric leakage of isotopically heavy nitrate in the eastern tropical Pacific during the last glacial period. Paleoceanography, 25(1), PA1204, https://doi.org/10.1029/2009PA001754
    Publication Date: 2023-05-12
    Description: We present new high-resolution N isotope records from the Gulf of Tehuantepec and the Nicaragua Basin spanning the last 50-70 ka. The Tehuantepec site is situated within the core of the north subtropical denitrification zone while the Nicaragua site is at the southern boundary. The d15N record from Nicaragua shows an 'Antarctic' timing similar to denitrification changes observed off Peru-Chile but is radically different from the northern records. We attribute this to the leakage of isotopically heavy nitrate from the South Pacific oxygen minimum zone (OMZ) into the Nicaragua Basin. The Nicaragua record leads the other eastern tropical North Pacific (ETNP) records by about 1000 years because denitrification peaks in the eastern tropical South Pacific (ETSP) before denitrification starts to increase in the Northern Hemisphere OMZ, i.e., during warming episodes in Antarctica. We find that the influence of the heavy nitrate leakage from the ETSP is still noticeable, although attenuated, in the Gulf of Tehuantepec record, particularly at the end of the Heinrich events, and tends to alter the recording of millennial timescale denitrification changes in the ETNP. This implies (1) that sedimentary d15N records from the southern parts of the ETNP cannot be used straightforwardly as a proxy for local denitrification and (2) that denitrification history in the ETNP, like in the Arabian Sea, is synchronous with Greenland temperature changes. These observations reinforce the conclusion that on millennial timescales during the last ice age, denitrification in the ETNP is strongly influenced by climatic variations that originated in the high-latitude North Atlantic region, while commensurate changes in Southern Ocean hydrography more directly, and slightly earlier, affected oxygen concentrations in the ETSP. Furthermore, the d15N records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50-70 ka.
    Keywords: IMAGES; International Marine Global Change Study
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 4
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    PANGAEA
    In:  Supplement to: Kienast, Stephanie S; Calvert, Stephen E; Pedersen, Thomas F (2002): Nitrogen isotope and productivity variations along the northeast Pacific margin over the last 120 kyr: Surface and subsurface paleoceanography. Paleoceanography, 17(4), 1055, https://doi.org/10.1029/2001PA000650
    Publication Date: 2023-05-12
    Description: Glacial-interglacial changes in sedimentary d15N over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical North Pacific (ETNP), where subsurface denitrification is active, to the Oregon margin, where no denitrification occurs today. Low d15N values (4-6 per mil) generally characterize glacial stages 2 and 4, and higher d15N values (7-10 per mil) are representative of the Holocene, millennial-scale periods within stage 3, and stage 5. The inferred synchroneity of d15N variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen-poor subsurface waters in the ETNP is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone. Similar to d15N, primary production indicators (percent Corg, Ba/Al, and percent opal) show glacial-interglacial as well as millennial-scale variations along the NE Pacific margin, with higher primary production during warm periods. However, the relative phasing between d15N and paleoproduction tracers within individual records changes latitudinally. Whereas d15N and primary production vary approximately synchronously in the midlatitudes, production lags d15N in the ETNP by several kiloyears. This lag calls for a new understanding of the processes driving denitrification in the ETNP. We suggest that oxygen input by the Equatorial Undercurrent as well as local organic matter flux controls denitrification rates in the ETNP. Moreover, the differences in relative timing point to a time-transgressive development of upwelling-favorable winds along the NE Pacific margin after the last glaciation, with those in the north developing several kiloyears earlier.
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 5
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    PANGAEA
    In:  Supplement to: Ganeshram, Raja S; Pedersen, Thomas F (1998): Glacial-interglacial variability in upwelling and bioproductivity off NW Mexico: Implications for Quaternary paleoclimate. Paleoceanography, 13(6), 634-645, https://doi.org/10.1029/98PA02508
    Publication Date: 2023-05-12
    Description: Sedimentary accumulation of biogenic components (organic carbon, opal, and biogenic barium) on the northwestern Mexican margin declined during every glacial interval of the past 140 kyr, indicating decreases in upwelling-induced productivity during cold periods. The glacial-interglacial contrasts in upwelling on this margin are attributed to reversals in land-ocean thermal contrast, the waxing and waning of the Laurentide Ice Sheet, and consequent responses of the western hemisphere wind fields. This scenario is consistent with three independent lines of evidence: terrestrial paleoclimatic data, general circulation model results, and our marine records. This pattern of glacial-interglacial variability in upwelling off NW Mexico is opposite to that observed in other low-latitude and midlatitude upwelling areas, such as the eastern equatorial Pacific. These results add to a growing pool of observations that the response of oceanic upwelling to glacial climatic forcing has been regionally variable.
    Type: Dataset
    Format: application/zip, 13 datasets
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  • 6
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    PANGAEA
    In:  Supplement to: Pedersen, Thomas F; Nielsen, B; Pickering, Mark (1991): Timing of Late Quaternary productivity pulses in the Panama Basin and implications for atmospheric CO2. Paleoceanography, 6(6), 657-677, https://doi.org/10.1029/91PA02532
    Publication Date: 2023-05-12
    Description: High-resolution percent Corg and delta18Oforam records obtained from Panama Basin core Atlantis II 54-25PC and additional data from nearby core P7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area. Both Corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods. Comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late Quaternary. The sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume (Sarnthein et al., 1988). The rapid decline in export production at the end of glacials in the equatorial Pacific may be attributed to the retreat of ice sheets (thus reduced wind velocities and upwelling) coupled with a coincident decline in atmospheric dust load and/or delivery rate. The Corg accumulation rate profiles do not correlate well with atmospheric CO2 records. For example, atmospheric CO2 was already at a minimum 40 kyr ago when production in the Panama Basin began increasing dramatically, commensurate with an increase in global dust levels. Using the relationship between the degree of photosynthetic fractionation and the concentration of free CO2 in the surface ocean postulated by Popp et al. (1989), delta13Corg measurements made on core P7 show that Panama Basin surface waters have been supplying CO2 to the atmosphere continually for at least the last 50 kyr. There is no evidence for a flux of CO2 into the surface ocean in this area at any time during this period despite the higher production. If the Panama Basin cores are representative of the eastern and central equatorial Pacific, then these observations weaken the influence on CO2 drawdown postulated for increased glacial productivity at low latitudes.
    Keywords: AT_II-054_25PC; ATII_USA; Atlantis II (1963); Core; CORE; P07; Panama Margin; PC; Piston corer
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 7
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    PANGAEA
    In:  Supplement to: Thunell, Robert C; Qingmin, Miao; Calvert, Stephen E; Pedersen, Thomas F (1992): Glacial-Holocene biogenic sedimentation Patterns in the South China Sea: productivity variations and surface water pCO2. Paleoceanography, 7(2), 143-162, https://doi.org/10.1029/92PA00278
    Publication Date: 2023-05-12
    Description: A bathymetric transect of cores in the South China Sea extending from 4200-m to less than 1000-m water depth has been examined for glacial-interglacial changes in carbonate and organic carbon sedimentation. Typical 'Pacific carbonate cycles' (high carbonate content during glacials and low carbonate content during interglacials) characterize cores from water depths deeper than 3500 m. In contrast, 'Atlantic carbonate cycles' (low carbonate during glacials and high carbonate during interglacials) are observed in cores from depths shallower than 3000 m as a result of increased dilution of carbonate by terrigenous material during glacial low stands of sea level. Glacial-interglacial changes in the carbonate chemistry of South China Sea intermediate and deep waters resulted in significant changes in the positions of the carbonate compensation depth (CCD) and the aragonite compensation depth (ACD). During the last glacial the CCD and ACD were at least 400 and 1200 m deeper, respectively, than at present. Organic carbon accumulation rates in the South China Sea were approximately 2 times higher during the last glacial than the Holocene. Carbon isotopic analyses and C/N ratios of the organic matter indicate that only a small fraction of the increase in glacial organic carbon accumulation can be attributed to input of terrestrial carbon. On the basis of this we conclude that surface water productivity in the South China Sea was approximately 2 times higher during the last glacial maximum. This is consistent with previous studies which have demonstrated that glacial productivity was higher in low- to mid-latitude regions of the Atlantic and eastern Pacific. The deglacial decrease in organic carbon accumulation is accompanied by a decrease in delta13Corg. Using the relationship between delta13Corg and [CO2](aq) developed by Popp et al. [1989], we estimate that surface water pCO2 values in the South China Sea during the last 25,000 years were very similar to atmospheric CO2 concentrations.
    Keywords: GGC; Giant gravity corer; MOANAWAVE01; MOANAWAVE02; MOANAWAVE03; MOANAWAVE04; MOANAWAVE06; MOANAWAVE09; MOANAWAVE10; MOANAWAVE11; MOANAWAVE12; MOANAWAVE13; South China Sea
    Type: Dataset
    Format: application/zip, 10 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: de Vernal, Anne; Pedersen, Thomas F (1997): Micropaleontology and palynology of core PAR87A-10: A 23,000 year record of paleoenvironmental changes in the Gulf of Alaska, northeast North Pacific. Paleoceanography, 12(6), 821-830, https://doi.org/10.1029/97PA02167
    Publication Date: 2023-05-12
    Description: Micropaleontological data of core PAR87A-10 reveal that the last glacial interval, prior to 13 ka, was marked by low biogenic fluxes and poor CaCO3 preservation. Quantitative estimates of sea-surface conditions based on dinocyst assemblages suggest that cold temperatures and freezing winter conditions existed during this period. The glacial to interglacial transition, i.e., the 13–8 ka interval, was characterized by an increase in fluxes of microfossils indicating enhanced productivity in surface waters. A higher biogenic carbonate production probably resulted in better preservation of CaCO3. This interval was marked by relatively low salinity and by sea-surface temperatures increasing toward modern values. Relatively high pollen flux during the transition suggests nutrient inputs through atmospheric and/or fluvial transport from the adjacent North American continent. After 8 ka, diminished fluxes of plankton, concomitant with a decline in pollen input, are associated with decreasing nutrient supply as predominantly eastward winds became established over the North Pacific.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 9
    Publication Date: 2023-05-12
    Keywords: AGE; Barium/Aluminium ratio; Carbon, organic, total; DEPTH, sediment/rock; Opal, biogenic silica; TC; Trigger corer; W8709A; W8709A-8TC; Wecoma; δ15N, nitrate
    Type: Dataset
    Format: text/tab-separated-values, 152 data points
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  • 10
    Publication Date: 2023-05-12
    Keywords: AGE; Barium/Aluminium ratio; Carbon, organic, total; Depth, corrected; DEPTH, sediment/rock; Opal, biogenic silica; PC; Piston corer; W8709A; W8709A-8; Wecoma; δ15N, nitrate
    Type: Dataset
    Format: text/tab-separated-values, 440 data points
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